Menard’s proposal to install stone columns for support of the MSE walls was both economical and time-saving as compared to other bids/approaches. In less than one month, Menard installed 126 stone columns (42-in in diameter) to an average depth of 20 ft. The design provided for 1 in of post-paving settlement, meeting the performance criteria of the project. In using lightweight fill for the MSE walls, an equivalent maximum bearing pressure of 1,400 psf was applied to the base of the wall. The stone columns were designed exclusively for settlement control, as bearing capacity was ensured by the use of the lightweight fill.
Of note: Due to the required construction sequence, work was done beneath an existing overpass. This low-overhead condition limited the depth of installation to 20 ft, which only partially treated the soft soil. This partial treatment, in combination with the lightweight fill used in the MSE wall, resulted in an optimized overall design. In addition to reducing the settlement, the stone columns also accelerated the settlement due to their high permeability, which allowed for faster paving of the ramps. A major challenge at the site was the presence of soft soil – which made it difficult to construct a suitable working platform. Menard worked closely with the general contractor to ensure work could proceed safely and productively. Another challenge was the occurrence of heave due to the installation of the large-diameter stone columns. Proper construction sequencing and coordination with the earthwork contractor to remediate soft spots on the site were critical to ensure a quality product and safe platform.
Notwithstanding all challenges, Menard successfully installed 126 stone columns to support two MSE walls as part of a major highway project in Illinois.